1. Field of the Invention
A sensor assembly for sensing human tissue in a protected area of a machine.
2. Description of the Prior Art
Automated manufacturing machines can pose a hazard to their human operators. These machines typically have moving components that may produce enormous forces and cause an operator injury. They are often outfitted with various forms of safety devices in order to reduce the danger to their human operators. These devices include emergency mechanisms that include a sensor and/or switch that sense operator presence in a protected area and produce as signal that is used to deactivate the machine, these include stop pushbuttons, safety latches, light beams, optical sensors, weight sensors, kick bars, belly bars, and pull bars, to name a few. However, these devices are often not optional in the applications in which they are implemented. Therefore, these devices are frequently used in various combinations in order to enhance the sensing of various hazardous conditions. Thus, these devices sometimes fail to give optimum protection for the operators. For example, they may afford protection for some hazards and not others. These problems are evident many applications, including a typical rubber mill.
A rubber mill utilizes at least one pair of rollers. The rollers of each pair are driven in mutually opposite directions. In normal operation, rubber is inserted (by the operator) into the rollers for flattening. This operation causes a potentially dangerous situation in which a worker can inadvertently get his or her fingers, hand or arm caught in the rollers. The roller construction, dimensions and spacing are sufficient to cause severe injury should this occur.
One approach to protecting an operator is disclosed in U.S. Pat. No. 6,376,939 (the '939 patent) to Suzuki et al. The '939 patent discloses a sensor apparatus having two electrodes disposed on opposite sides of a protected area of a machine. Material being fed into the machine must pass between the two plates. A circuit detects capacitance change between the electrodes as objects pass between the two plates. A monitor then attempts to determine whether the object includes human tissue.
Unfortunately, due to the planar separation of the electrodes, space restrictions make the sensor apparatus of the '939 patent can be difficult to implement in many machines. Furthermore, the apparatus may not be able to detect human tissue that is embedded within a dielectric, such as the rubber sheets that are being fed into the rollers of the rubber mill by the operator.
There remains an opportunity for a sensor apparatus which can be implemented in machines having two or three dimensional protected areas or spaces where it is desirable to detect human or other animal tissue within these areas or spaces. Still further, there remains an opportunity for an apparatus which can detect the presence of such tissues in the presence of other materials, such as dielectric materials, and particularly in the presence of rubber.